Rapid settling of a colloidal gel

Abstract

We study the rapid collapse of gels formed from strongly aggregating colloidal suspensions. This gravity-driven collapse is associated with the apparition of fractures in the bulk of the gels that provide an easy route to the gel-supernatant interface for the solvent and are the cause for the strong increase of the settling velocity. We propose a model that connects the apparition of a fracture in the gel to the settling velocity of the interface. This description takes into account the microscopic structure of the gel and is consistent with the experimental results.

Thermal Jamming of a Colloidal Glass

“…As predicted by Sollich [9] and also observed experimentally [14,15] the shear stress in a flow start-up experiment for a soft glass goes through an overshoot before reaching its steady-state value. Although the origin of the overshoot is not clearly understood, it is believed to reflect the breaking of cages in a jammed system.…”

“…Mechanical rheometry in oscillatory-and transient shear flow, using an Anton Paar MCR 501 rheometer equipped with cone and plate fixture, was used to characterize the flow behavior of the material. All measurements were performed at temperatures above the glass transition temperature of polyisoprene and samples were presheared to erase any shear history, with the waiting time after the preshearing kept long compared to the measurement time to ensure that the measurements are not affected by aging [14].…”

Highly Nonlinear Dynamics in a Slowly Sedimenting Colloidal Gel

“…A full decay of the ICF indicates particle rearrangements over a lengthscale q −1 = 0.66R. Thus, we are able to measure simultaneously and with both temporal and spatial resolution the local volume fraction, sedimentation velocity and microscopic relaxation dynamics, in contrast to previous works were only the total gel height, h(t) [6,7,[10][11][12], or at most ϕ(z, t) [9,21] could be measured. Figure 1 illustrates the time dependence of h(t), ϕ(z, t), and v(z, t), where z = 0 is the cell bottom.…”

“…Although they exhibit solid-like mechanical properties, colloidal gels are easily disrupted by small perturbations, such as gravitational forces. While a large body of macroscopic observations of gels under gravitational stress exists [5][6][7][8][9][10][11][12][13], very little is known on the microscopic processes at play during sedimentation, thus limiting our ability to understand and predict the behavior of sedimenting gels.Here, we use a novel light scattering method to gain access to the dynamics of a slowly settling colloidal system from the macroscopic deformation of the sample down to the relaxational behavior at the particle scale. We find that the very slow macroscopic deformation occurs via irreversible plastic events at the microscopic scale.…”

Sudden collapse of a colloidal gel

“…Sudden or 'delayed' network collapse is observed in a wide variety of materials [7][8][9][10][11][12][13][14][15][16] and seems to be ubiquitous at small U c /k B T . However, while sudden collapse * Corresponding author:P.Bartlett@bristol.ac.uk has been attributed to channel formation within the gel [12,13], the microscopic processes operating have never been fully established. A better microscopic understanding of the origin of sudden gel collapse is important not only because the distinctive settling behavior is intriguing from a scientific viewpoint but also because a quantitative prediction of gel stability is a critically important issue in the formulation and manufacture of many commercial products.…”